I pushed a Makefile for KL25Z mbed with ARM GCC to my github Makefile [https://github.com/0xc0170].
I intended to use only eclipse with all those available options. It turned out it was time-consuming to set everything correctly, therefore I wrote this makefile which made everything easier. Small modification should allow you to use it on different targets. I have seen gcc4mbed but that was too much files for my taste. The makefile follows the directory structure which is at the moment. It has changed recently and will be different I believe soon again.
Files which are used are not yet a part of mbed, I am still facing a problem with binary created. It just locks KL25Z and does not run. I'll prepare an article how to debug KL25Z in eclipse with mbed.